Routers are communications networking devices that forward data packets between computer networks. As such, a router typically includes at least one data line from each of two or more computer networks.
Routers direct traffic between and among computer networks, typically forwarding data packets from one router to another router until a destination node is reached. When a data packet is received on one of the data lines, the router typically reads address information in the packet to determine its destination node. The router then uses information, such as a routing table, to direct the packet to the next node (e.g., another router) on its way to the destination node.
Routers can be simple, connecting a home computer to an internet service provider. Other routers are more complex, connecting large networks to core routers for high speed data transfer over fiber optic trunks. Routers can be employed in various topologies.
Routers and other communications networking devices typically include interface devices for communications with other routers (or other communications devices). Such devices may be used, for example, to interface a network device motherboard to a fiber optic cable for communications with another network device. Interface devices used to interface a network device to a fiber optic cable can be referred to as optical interface devices, or optical transceivers. A router is a convenient example of a communications networking device, however network devices which use optical interface devices can include routers, switches, hubs, or other networking components.
One example of an optical interface device is a Quad Small Form-factor Pluggable (“QSFP”) transceiver. A QSFP is a compact, hot-pluggable transceiver used for data communications applications. The form factor and electrical interface are specified by a QSFP multi-source agreement (“MSA”) under the auspices of the Small Form Factor Committee. The QSFP follows an industry format jointly developed and supported by many network component vendors. The format specification is evolving to enable higher data rates. As of May 2013, the highest possible rate for a QSFP interface device is 4×28 Gbit/s (referred to as “QSFP28”).
The form factor of a QSFP28 transceiver is constrained in size in order to enable a number of such transceivers to be installed in a panel of a router or switch, providing a suitable amount of bandwidth density in a given amount of space. Because of the exterior size constraint of the QSFP28 form factor, the size and capability of components within the transceiver is limited. For example, a laser within the QSFP28 transceiver would be limited in power due to a limitation on its size and/or a limitation on the amount of heat possible to dissipate for the size of the transceiver. It is noted that the form factor also only permits one optical fiber input, and one optical fiber output.
Generations of refinements of this interface have led to highly power-optimized components designed to fit within this form factor. However due to the limitations imposed on its capabilities by its size constraint, a current QSFP28 transceiver only provides the capability to send data over an optical fiber for a limited distance (possibly 1 km or so) to another router port or to a long-distance transmission box.
In order to satisfy datacenter interconnect needs, an additional transceiver, having a client-facing interface connected to a line-facing interface, can be used to boost the reach of the QSFP transceiver. This additional transceiver, which can be referred to as a “gray” interface, can be effective but can require the customer to buy two transceiver devices for each desired line interface, increasing costs. The optical fiber reach that can be achieved with such client interfaces can be ˜10 km for a laser wavelength of 1310 nm. However, the gray interface typically can only support one 100G interface. The interconnection bandwidth required in a data center is high however, and interfaces supporting on the order of a terrabit of data would be preferred to a 100G interface.
For this reason, it may be preferable to transmit data over the optical fiber using Dense Wavelength Division Multiplexing (DWDM). In some cases, DWDM can allow 40 channels of 100G on one fiber when using PAM4 modulation. However, the digital signal processor (DSP), forward error correction (FEC), and laser powers are all higher for 100G PAM4 over longer links at 1550 nm with stringent wavelocking requirements. This total added power can exceed the thermal capability of a QSFP28 (or other optical transceiver) however. Accordingly, it may be desired to provide an optical transceiver capable of outputting laser light at a higher power while maintaining current form factor limitations.